The invention relates to a continuous process for producing aluminium, e.g. alkoxides by reacting aluminium in comminuted form with an excess of aliphatic C.sub.3 to C.sub.10 -alcohol, in which the aluminium being fed from above into a reactor is contacted on or above a perforated plate or screen with an aluminium alkoxide/alcohol mixture.
When reacting aluminium and anhydrous alcohol for producing metal alkoxides (also called alcoholates), due to the high heat of reaction occuring during this reaction, there are considerable problems both when reacting large quantities and when the process is performed continuously. Such problems are caused, for example, by unequal aluminium metering or due to the fact that part of the aluminium only reacts after a certain time, accompanied by the momentary release of large quantities of heat.
To eliminate these problems, U.S. Pat. No. 2,845,447 for example, proposes carrying out the reaction not with an excess of alcohol but with an excess of aluminium in the liquid phase. The aluminium in the reactor is contacted with a mixture of aluminium alkoxide and alcohol in the lower area of the reactor and the resulting aluminium alkoxide with the as yet unreacted alcohol is in part supplied back to the reactor circuit and in part is separated. In this process with excess aluminium, as a result of pressure fluctuations or for other reasons, suddenly larger quantities of the alcohol-aluminium alkoxide mixture can come into contact with the aluminium and consequently release large quantities of heat, which can overload the plant. In addition, lower reaction rates can result from working with substoichiometric alcohol quantities and as a result the yield is reduced.
Similar problems with respect to the reaction control occur in a process according to U.S. Pat. No. 2,666,076, in which working takes place with an excess of aluminium alkoxide/alcohol mixture in the reactor and aluminium granulate is continuously supplied from above into the said reactor.
In another but discontinuous process according to German Pat. No. 930,087, the aluminium is present in comminuted form on a screen plate of a reactor and is contacted with alcohol introduced into the reactor. When the reaction gets out of control the liquid phase is forced into an expansion vessel as a result of the hydrogen overpressure which occurs, so that the liquid phase is separated from the aluminium present on the screen plate. This process operates with an alcohol excess and in the case of a reverse flow of the liquid phase, there can be a reaction which is difficult to control and is excessive.
The object of the invention is to propose a process for producing aluminium alkoxides, which can be continuously performed in trouble-free manner with good yields and in which the liquid phase is immediately separated from the aluminium if a fault occurs. In addition, the process according to the invention, unlike the aforementioned and other known processes, makes it possible to use normal grade aluminium instead of aluminium activated by addition of further metals or metal compounds, and also pure alcohols can be used, i.e. the alcohol desired for alkoxide formation, without, as has often been proposed, having to introduce heavier hydrocarbons into the liquid phase for controlling the reaction, which ensures the purity of the end product.